OPEN-FILE REPORT 92


 LITHOSTRATIGRAPHIC UNITS

 Tertiary System

Eocene Series
 Avon Park Formation

 The Middle Eocene Avon Park Formation (Tap), first described by Applin and Applin
(1944), is the oldest unit investigated in the present study area. The unit, which only occurs in the
subsurface in the study area, consists of cream to light-brown to tan, poorly-indurated to well-
indurated, variably fossiliferous limestone (grainstone to wackestone, with rare mudstone). The
limestones are interbedded with tan to brown, very poorly-indurated to well-indurated, very fine
to medium crystalline, fossiliferous (molds and casts), vuggy dolostones. Fossils present in the
unit include mollusks, foraminifera, echinoids, algae and carbonized plant remains.
 The Avon Park Formation was only encountered in a few wells in the study area. The top
of the Avon Park ranges from 177 feet (53.9 meters) below MSL in W-18832 to 165 feet (50.3
meters) below MSL in W-4497 (cross-section G-G' on OFMS 99-02). No wells utilized for
cross-sections penetrated the entire section of the Avon Park Formation. The Avon Park
Formation forms part of the FAS (Southeastern Geological Society Ad Hoc Committee on
Florida Hydrostratigraphic Unit Definition, 1986).

 Ocala Limestone

 The Upper Eocene Ocala Limestone (To), first described by Dall and Harris (1892), is a
biogenic marine limestone comprised largely of foraminifera, mollusks, echinoids and
bryozoans. The unit, which sits unconformably on the Avon Park Formation, may be dolomitized
to varying degrees within the study area, making the contact between the two units difficult to
discern in cuttings. Based on lithologic differences, the Ocala Limestone can be informally
subdivided into an upper and lower unit (Scott, 1991a). This subdivision, while often apparent in
cores and quarries, is difficult to ascertain in cuttings. As a consequence of this, the geologic
cross sections do not break out the upper and lower Ocala Limestone.
 The upper unit is typically a white to cream, fine- to coarse-grained, poorly- to well-
indurated, poorly-sorted, very fossiliferous limestone (wackestone, packstone, and grainstone).
Fossils commonly include foraminifera, bryozoans, mollusks, and a rich diversity of echinoids.
The lower unit is typically a white to cream, fine- to medium-grained, poorly- to moderately-
indurated limestone (grainstone to packstone). Fossils include foraminifera, bryozoans, algae,
mollusks, echinoids, and crabs.
 The top of the Ocala Limestone, which is often karstified, ranges from 42 feet (12.8
meters) above MSL in W-15930 (cross sections C-C' and G-G' on OFMS 99-02) to 89 feet (27.1
meters) below MSL in W-620 (cross section D-D' on OFMS 99-02). Only a few wells penetrated
the entire thickness of the Ocala Limestone in the study area. In these wells, the thickness of the
Ocala Limestone ranges from 155 feet (47.2 meters) in W-4497 (cross-section G-G' on OFMS
99-02) to a projected thickness of 215.5 feet (65.7 meters) in W-15930 (cross-section G-G' on
OFMS 99-02). The Ocala Limestone is unconformably overlain by the Suwannee Limestone
(Ts) throughout the study area. The Ocala Limestone forms part of the FAS (Southeastern
Geological Society Ad Hoc Committee on Florida Hydrostratigraphic Unit Definition, 1986).